Growing evidence suggests that contrary to popular belief, schools mostly do not generate achievement gaps in cognitive skills but, rather, reflect the inequalities that already exist. In the case of socioeconomic status, exposure to school often reduces gaps. Surprisingly little is known, however, about whether this pattern extends to gender gaps in cognitive skills. We compare how gender gaps in math and reading change when children are in school versus out (in the summer) among over 900,000 U.S. children. We find that girls learn faster than boys when school is out (in both reading and math), but this advantage is completely eliminated when school is in session. Compared to the family environment, schools act as a relatively standardizing institution, producing more similar gendered patterns in learning.